A Review on the Role of miR-149-5p in the Carcinogenesis

miR-149 is an miRNA with essential roles in carcinogenesis. This miRNA is encoded by the MIR149 gene on 2q37.3. The miR-149 hairpin produces miR-149-5p and miR-149-3p, which are the “guide” and the sister “passenger” strands, respectively. Deep sequencing experiments have shown higher prevalence of miR-149-5p compared with miR-149-3p. Notably, both oncogenic and tumor suppressive roles have been reported for miR-149-5p. In this review, we summarize the impact of miR-149-5p in the tumorigenesis and elaborate mechanisms of its involvement in this process in a variety of neoplastic conditions based on three lines of evidence, i.e., in vitro, in vivo and clinical settings.


Introduction
MicroRNAs (miRNAs) are a group of small-sized regulatory noncoding RNAs which bind to the 3 -UTR of target mRNAs in a specific manner to inhibit their translation [1]. miRNAs can affect diverse aspects of carcinogenesis, tumor evolution, metastatic and angiogenic processes, and resistance to chemoradiotherapeutics [2]. miR-149 is an miRNA with essential roles in carcinogenesis. This miRNA is encoded by MIR149 gene on 2q37.3. The miR-149 hairpin produces miR-149-5p and miR-149-3p which are the "guide" and the sister "passenger" strands, respectively [3]. These two miRNAs have completely dissimilar sequences, suggesting their distinct roles in biological processes [3]. Deep sequencing experiments have shown a higher prevalence of miR-149-5p compared with miR-149-3p.
Physiological functions of miR-149-5p have been evaluated by researchers. For instance, it has been shown to be up-regulated in bovine adipocytes in certain times during their differentiation. The functional role of miR-149-5p in this process is exerted through targeting CRTC1 and CRTC2 [4]. Moreover, the expression of miR-149-5p has been found to be decreased in PDGF-BB-induced vascular smooth muscle cells. Up-regulation of miR-149-5p could suppress the proliferation, invasion and migration of vascular smooth muscle cells, whereas its silencing has the opposite effect. Moreover, histone deacetylase 4 (HDAC4) is the miR-149-5p target, through which this function of miR-149-5p is accomplished [5].
Notably, both oncogenic and tumor suppressive roles have been reported for miR-149-5p. In this review, we summarize the impact of miR-149-5p in tumorigenesis and elaborate mechanisms of its involvement in this process in a variety of neoplastic conditions based on three lines of evidence, i.e., in vitro, in vivo and clinical settings.

Gastrointestinal Tumors
A high throughput sequencing experiment in gastric cancer has shown down-regulation of the circular RNA (circRNA) circNRIP1. This circRNA has been shown to act as a sponge for miR-149-5p. This miRNA regulates metabolic pathways through AKT1/mTOR axis. miR-149-5p suppression has been shown to exert similar effects with up-regulation of circNRIP1 in gastric cancer cells [6]. Another study in gastric cancer has shown downregulation of miR-149-5p parallel with the up-regulation of the long non-coding RNA (lncRNA) BLACAT1 and KIF2A. miR-149-5p has been shown to be sponged by BLACAT1, leading to the up-regulation of KIF2A [7]. Moreover, miR-149-5p has been demonstrated to be sponged by circNHSL1. In fact, the effects of circNHSL1 on cancer cell migration, invasiveness and glutaminolysis is mediated through sponging miR-149-5p. Experiments in gastric cancer cells have led to identification of YWHAZ as the target of miR-149-5p [8].
Two independent studies have shown the sponging effects of LINC00460 on miR-149-5p in the context of colorectal cancer. LINC00460/miR-149-5p has important functions in the regulation of expression of p53 [9] and BGN [10] in this type of cancer.
In addition, miR-149-5p has been found to be sponged by circCTNNA1, a circRNA with pro-proliferative and pro-migratory effects in colorectal cancer cells. miR-149-5p has been shown to decrease the expression of FOXM1. Thus, the circCTNNA1/miR-149-5p/FOXM1 axis has been suggested as a target for therapeutic interventions in colorectal cancer [11]. miR-149-5p has also been shown to be sponged by other oncogenic non-coding RNAs such as PCAT1 [12], DLGAP1-AS1 [13] and circ5615 [14] in colorectal cancer cells.

Thyroid Cancer
miR-149-5p has a tumor suppressor role in medullary thyroid carcinoma through directly targeting GIT1. miR-149-5p up-regulation could inhibit the proliferation and invasive properties of medullary thyroid carcinoma cells [15]. In papillary thyroid cancer, miR-149-5p has been shown to bind with circ-FLNA, a circRNA whose expression is regulated by TR4. Binding of circ-FLNA with this miRNA releases MMP9 from the inhibitory effects of miR-149-5p. Thus, the TR4/circ-FLNA/miR-149-5p/MMP9 axis has been identified as an important player in the pathogenesis of papillary thyroid cancer [16].

Oral Cancer
Expression of miR-149-5p has been shown to be reduced in oral squamous cell carcinoma cells, particularly in cisplatin resistant cells. Up-regulation of miR-149-5p could enhance the cytotoxic effects of this drug in both resistant cells and parental cells. miR-149-5p could also decrease the proliferation, migratory aptitude and invasiveness of both cell lines, and promote their apoptosis through decreasing expression of TGFβ2 [17]. In this kind of cancer, miR-149-5p has been shown to be sponged by DLEU1 lncRNA. Since miR-149-5p could decrease the expression of CDK6, down-regulation of miR-149-5p by this lncRNA leads to up-regulation of CDK6 and a subsequent increase in cell proliferation and cell cycle progression [18].

Ovarian Cancer
In ovarian cancer, two different studies have shown contradictory results about the role of miR-149-5p. Xu et al. have shown that miR-149-5p silencing increases the sensitivity of ovarian cancer cells to cisplatin. miR-149-5p has been found to target the most important kinase elements of the Hippo signaling pathway, i.e., MST1 and SAV1, leading to the inactivation of TEAD expression [19]. Conversely, Li et al. have shown a tumor suppressor role for miR-149-5p in ovarian cancer cells through targeting FOXM1 [20].

Osteosarcoma
Expression of miR-149-5p has been found to be decreased in osteosarcoma cells. Forced up-regulation of miR-149-5p has inhibited the growth of these cells through targeting TNFRSF12A. The anti-proliferative impacts of miR-149-5p are exerted through modulation of the PI3K/AKT pathway [21].

Breast Cancer
Expression of miR-149-5p has been found to be down-regulated in breast cancer cells, parallel with the up-regulation of circ_0072995 and SHMT2 levels. This miRNA has a role in the regulation of anaerobic glycolysis through the suppression of SHMT2 expression [22].
Another experiment in breast cancer cells has shown that the anesthetic agent propofol can alter resistance to trastuzumab via modulation of the IL-6/miR-149-5p molecular axis. Authors have reported production of high levels of IL-6 and IL-8 cytokines, were released by resistant cells, induction of the stemness phenotype mammospheres and enhancement of epithelial-mesenchymal transition (EMT) in trastuzumab resistant cells. Notably, propofol could inhibit all of these processes through the up-regulation of miR-149-5p and subsequent down-regulation of IL-6 expression [23]. Another study has shown the effects of ursolic acid in the attenuation of the paclitaxel resistance phenotype in breast cancer cells through influencing the miR-149-5p/myd88 axis [24].

Urogenital Cancers
In prostate cancer cells, hsa-miR-149-5p has been found to suppress tumorigenic processes through inhibiting expression of RGS17 [25].
In bladder cancer cells, the anti-cancer effect of miR-149-5p is exerted through the inhibition of expression of RNF2. Notably, miR-149-5p has been shown to be sponged by the oncogenic circRNA_100146 in these cells [26]. Figure 1 shows the tumor-suppressive role of miR-149-5p in esophageal cancer, bladder cancer, breast cancer, ovarian cancer, thyroid cancer and colorectal cancer.
important kinase elements of the Hippo signaling pathway, i.e., MST1 and SAV1, leading to the inactivation of TEAD expression [19]. Conversely, Li et al. have shown a tumor suppressor role for miR-149-5p in ovarian cancer cells through targeting FOXM1 [20].

Osteosarcoma
Expression of miR-149-5p has been found to be decreased in osteosarcoma cells. Forced up-regulation of miR-149-5p has inhibited the growth of these cells through targeting TNFRSF12A. The anti-proliferative impacts of miR-149-5p are exerted through modulation of the PI3K/AKT pathway [21].

Breast Cancer
Expression of miR-149-5p has been found to be down-regulated in breast cancer cells, parallel with the up-regulation of circ_0072995 and SHMT2 levels. This miRNA has a role in the regulation of anaerobic glycolysis through the suppression of SHMT2 expression [22].
Another experiment in breast cancer cells has shown that the anesthetic agent propofol can alter resistance to trastuzumab via modulation of the IL-6/miR-149-5p molecular axis. Authors have reported production of high levels of IL-6 and IL-8 cytokines, were released by resistant cells, induction of the stemness phenotype mammospheres and enhancement of epithelial-mesenchymal transition (EMT) in trastuzumab resistant cells. Notably, propofol could inhibit all of these processes through the up-regulation of miR-149-5p and subsequent down-regulation of IL-6 expression [23]. Another study has shown the effects of ursolic acid in the attenuation of the paclitaxel resistance phenotype in breast cancer cells through influencing the miR-149-5p/myd88 axis [24].

Urogenital Cancers
In prostate cancer cells, hsa-miR-149-5p has been found to suppress tumorigenic processes through inhibiting expression of RGS17 [25].
In bladder cancer cells, the anti-cancer effect of miR-149-5p is exerted through the inhibition of expression of RNF2. Notably, miR-149-5p has been shown to be sponged by the oncogenic circRNA_100146 in these cells [26]. Figure 1 shows the tumor-suppressive role of miR-149-5p in esophageal cancer, bladder cancer, breast cancer, ovarian cancer, thyroid cancer and colorectal cancer.

Lung Cancer
In lung cancer cells, miR-149-5p has been found to down-regulate the expression of B3GNT3, an oncogene that influences lung cancer cell proliferation and invasiveness [27]. Moreover, expression of this miRNA has been found to be decreased by HOTAIR [28], HNF1A-AS1 [29] and MIAT [30] lncRNAs in these cells. In fact, HOTAIR has been shown to induce cisplatin resistance and increase the proliferation, migratory potential and invasiveness of cisplatin-resistant lung cancer cells through targeting miR-149-5p [31].
Another study on lung cancer cells has shown the role of miR-149-5p in the enhancement of the response to gefitinib. The oncogenic lncRNA LINC00460 has been found to promote resistance to EGFR-TKI through sequestering miR-149-5p, thus increasing IL-6 levels and facilitating EMT process [32]. Conversely, comparison of miRNA profiles in gefitinib-resistant human lung cancer cells and the parental cells has shown up-regulation of miR-149-5p in resistant cells. miR-149-5p mimics could reduce the motility of lung cancer cells. Up-regulation of miR-149-5p could efficiently evaluate the half maximal inhibitory concentrations of the cell following treatment with gefitinib. Besides, expressions of miR-149-5p in both cell lines have been inversely correlated with caspase-3 levels. Taken together, miR-149-5p expression is increased in the gefitinib-resistant human lung cancer cells contributing in the acquired resistance to gefitinib [33].
Moreover, over-expression of miR-149-5p in cancer-derived exosomes could enhance growth of tumor cells and inhibit their apoptosis through suppression of AMOTL2 levels [34].

Hepatocellular Carcinoma
In hepatocellular carcinoma, M2 macrophages have been shown to increase the invasiveness and migratory potential of cancer cells through decreasing miR-149-5p levels and subsequent activation of MMP9 signaling [35]. In this kind of cancer, miR-149-5p can enhance response to sorafenib through decreasing AKT1 levels [36]. Moreover, it can exert anti-cancer effects through decreasing MAP2K1 expression [37].
miR-149-5p has also been shown to target 3'-UTR of the MTHFR transcript. Expression of miR-149-5p has been shown to be increased in both normal hepatocytes and hepatocellular carcinoma cells in response to folic acid deficiency. However, this condition has resulted in different responses in the expression of MTHFR in these two cell lines. In fact, MTHFR levels are reduced in cancerous cells but remained constant in normal hepatocytes in response to folic acid deficiency. Thus, miR-149-5p exerts distinct post-transcriptional influences on this gene upon folic acid deficiency in normal hepatocytes and hepatocellular carcinoma cells. Moreover, this miRNA may have an anti-cancer effect in longstanding folic acid deficiency conditions [38].
In vivo studies have shown the impact of miR-149-5p in the facilitation of the inhibitory function of propofol against lung metastases in a breast cancer xenograft model [23]. On the other hand, miR-149-5p has been shown to exert oncogenic effects in ovarian cancer, since its silencing has decreased tumor volume and resistance to cisplatin [19]. Table 2 shows the role of miR-149-5p or miR-149-5p-intercating genes in carcinogenesis based on animal models. Table 2. Role of miR-149-5p or miR-149-5p-intercating genes in the carcinogenesis based on animal models (∆: knock-down or deletion, ↑: up-regulation or enhancement, ↓: down-regulation, CDDP: cisplatin, UA: ursolic acid, PTX: Paclitaxel).
In bladder cancer, both tumor suppressor [26] and oncogenic [49] effects have been reported for mR-149-5p. In ovarian cancer, miR-149-5p has been shown to be up-regulated in cancerous tissues, particularly chemoresistant ones compared with controls [19]. However, another study has shown up-regulation of circPVT1, a miR-149-5p-sequestering circRNA in this type of cancer [20]. In lung cancer, while most studies have indicated a tumor suppressor role for miR-149-5p (Table 3), assessment of a GEO dataset has shown up-regulation of this miRNA in cancer patients compared with controls [34]. Table 3. Role of miR-149-5p or miR-149-5p-interacting genes in carcinogenesis based on clinical studies (OS: Overall survival, DFS: disease-free survival, PFS: progression-free rate TNM: tumornode-metastasis, ANCTs: adjacent non-cancerous tissues, NSCLC: non-small cell lung cancer, ccRCC: clear cell renal cell carcinoma).

Reference
Gastric cancer (GC)
Clinical studies have suggested a tumor suppressor role for mR-149-5p in gastric, liver, colorectal, medullary/papillary thyroid, breast, prostate, esophageal, renal, cervical and oral squamous cell cancers as well as osteosarcoma. In bladder and ovarian cancers, both tumor-suppressor and oncogenic effects have been reported for mR-149-5p. In lung cancer, while most studies have indicated a tumor-suppressor role for miR-149-5p, a single study has shown up-regulation of this miRNA in cancer patients compared with controls. Thus, most conducted studies are in favor of a tumor-suppressor role for mR-149-5p. However, a context-dependent role might be considered for this miRNA. Consistent with the tumor-suppressor role for this miRNA, several studies have shown correlation The pink octagon and green ellipse indicate lncRNAs and miR-149-5p, respectively. The graph visualization was constructed by Cytoscape version 3.6.1.
The impact of miR-149-5p in carcinogenesis has been appraised by a number of in vitro and in vivo studies which have silenced this miRNA or the related lncRNAs/circRNAs. This miRNA can affect the responses of cancer cells to oxaliplatin, cisplatin, 5-fluouracil, sorafenib, gefitinib and trastuzumab.
Clinical studies have suggested a tumor suppressor role for mR-149-5p in gastric, liver, colorectal, medullary/papillary thyroid, breast, prostate, esophageal, renal, cervical and oral squamous cell cancers as well as osteosarcoma. In bladder and ovarian cancers, both tumor-suppressor and oncogenic effects have been reported for mR-149-5p. In lung cancer, while most studies have indicated a tumor-suppressor role for miR-149-5p, a single study has shown up-regulation of this miRNA in cancer patients compared with controls. Thus, most conducted studies are in favor of a tumor-suppressor role for mR-149-5p. However, a context-dependent role might be considered for this miRNA. Consistent with the tumor-suppressor role for this miRNA, several studies have shown correlation between the down-regulation of this miRNA and shorter survival of patients, indicating a role for miR-149-5p as a prognostic predictor.
Cumulatively, miR-149-5p partakes in a complex functional network which is constructed by several cancer-related lncRNAs and circRNAs. This network efficiently controls the activity of several cancer-related signaling pathways. Modulation of expression of miR-149-5p can be regarded as a therapeutic modality for the attenuation of cancer cells' growth and the induction of chemosensitivity in these cells.
In conclusion, miR-149-5p is an example of miRNAs with important physiological roles whose expression has been dysregulated in various types of cancer. Future studies should focus on the design of targeted therapies for the amendment of dysregulation of this miRNA.